We have all heard rumors about performance version of Model S with accelerations that rival Roadster.
Well, I saw in autobloggreen Nissan Leaf-based race car (NISMO RC) and found it basically comical (it is way too slow to be such thing), but following discussion brought up a old Subaru Imprezza -conversion that successfully beat its ICE counterparts in racing (http://proev.com/MDetail3.htm). However that Subaru was nowhere close as impressive that even basic Model S is.
I would think that racing version of Model S is more than doable, and it would be great to see it in the track. It would just need a bit more top speed to be really competitive with ICE cars.